National Weather Service San Juan PR
438 AM AST Sun Jun 21 2020
.SYNOPSIS...
The big story for the next several days will the dense Saharan
dust event. Along with the dust, dry air will lead to fairly calm
weather for the next several days. The next tropical wave is
expected to arrive Thursday night. Marine conditions will be
choppy due to moderate to fresh easterly winds associated with the
tropical wave leaving the region today and a fairly strong
surface high in the central to east Atlantic.
&&
.SHORT TERM...Today through Tuesday...
A drying trend will continue as the lingering moisture of
yesterday`s tropical wave exits the region. A dense air mass with
suspended African dust particles will create hazy skies and poor
visibilities across the northeast Caribbean through the morning
hours, reaching the U.S. Virgin Islands and Puerto Rico by this
afternoon into the first part of this week. The peak of this event
is forecast between late tonight and early Monday, lasting until at
least mid-week. This weather pattern will promote above-normal
overnight temperatures (in the low-80s), making it easier to reach
high temperatures in the low to mid-90s each afternoon.
.LONG TERM...Wednesday through Monday...
By Wednesday, the worst of the dust should be behind us, though
moderate amounts of dust are expected for the full duration of the
long-term period. Some moisture will drop in for Wednesday and
Thursday from the north associated with an old front. The moisture
does not look like much at this point, but showers should be able to
develop over southwest PR under northeasterly flow for Wednesday,
though these showers will likely be unimpressive. Thursday however
looks better for showers and thunderstorm development. A trough at
upper levels is still expected to develop to our west, that will
enhance shower and thunderstorm activity. With winds switching more
from the southeast, winds will converge over the northwestern
portion of PR in the afternoon, so that is where the activity should
be.
Friday looks even more interesting as a tropical wave is expected to
move through the area, and may also be enhanced by the upper-
level trough to the west. The GFS model is projecting a more
robust wave compared to yesterday, but the European model has a
less impressive wave than what it was simulating yesterday with
most of the moisture exiting the region by Friday afternoon. With
still plenty of time before its arrival, more changes to the
forecast of this wave are probable. Thereafter however, dry
conditions are once again expected to prevail through the weekend
and into the next week with only weak patches of moisture riding
in on the easterly trade winds.
&&
.AVIATION...
VFR conditions will prevailed. However, a dense Saharan air mass
will reduce VIS after 21/18z across the local flying area between 6-
9 SM and diminishing overnight into Monday. Calm to light and VRB
winds will prevail thru 21/13z, then will return from the ESE at 10-
20 kt with higher gusts and sea breeze variations.
&&
.MARINE...
Moderate to fresh winds will continue for the next several days,
leading to choppy seas up to 5 to 6 feet. At this point, it
appears Small Craft Advisory conditions may be met for Monday
night and into Tuesday due to the windy conditions, and the
decision to put that advisory out will be made in the next 24
hours. Regardless, small craft operators are urged to exercise
caution. Finally, expect lower visibility due to Saharan dust.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 92 79 91 80 / 20 20 20 20
STT 92 82 91 80 / 20 20 10 20